In a conventional sound reproduction device, which receives sound signals transmitted via analog radio communication, noise level increases in the reproduced sounds as radio wave propagation condition worsens. Listeners therefore may recognize degree of degradation of the radio wave propagation condition. The recent digital communication technology, software demodulation technology, etc. improves quality of reproduced sounds. As a result, sounds are reproduced without noises if the radio wave propagation path is in a condition acceptable to reproduce sounds. Sounds sometimes break up if the radio wave propagation path is not in the acceptable condition. In the case that the sound reproduction device is a mobile type like a cellular phone, the radio wave propagation condition is likely to worsen if the device is moved into a weak electric field area. Therefore, it is desired to notify users of degrading propagation condition so that quality of the sound reproduction is not degraded.
In cellular phones, as disclosed in JP-A-3-192129, alarm sounds are added to the sounds when the radio wave propagation condition degrades in the middle of communication. Alternatively, as disclosed in JP-A-8-139663 and JP-A-11-122197, pseudo noises varying with the level of degradation of the propagation condition are added to the sounds.
In sound reproduction devices like a radio receivers that reproduce voice sounds or music sounds, the alarm sounds or pseudo noises will lower the reproducibility of sounds and artistic quality of music.